Thanks for the info Larry, I don't have a registry and do not intend to buy one (rodneym)
So the condition of the substructure and body determines degree of originality, essentially what AC provided and the degree that it has remained in tact (my take on it). Motor, transmission and rearend accountability not part of it. I wonder if 2nd gen vettes (1963–1967) follow a similar criteria, just a curiosity and nothing more. That matching number guide for GM classics I mentioned earlier had a vette section in it with the same traceability info as the GTO.